Redescription of ‘<i>Amyzon</i>’ <i>brevipinne</i> and remarks on North American Eocene catostomids (Cypriniformes: Catostomidae)

The Eocene catostomid fish (Cypriniformes: Catostomidae) from the Allenby Formation, British Columbia, Canada, is reviewed and revised based on recently collected specimens. The fish was originally recognized as a catostomid by Cope in 1893 and described as <i>Amyzon brevipinne</i>. Wilson comprehensively redescribed the species in 1977 based on a large collection. More specimens collected recently brought to light the need for a systematic revision of this species, different from all known <i>Amyzon</i> species in having a narrow frontal bone with elongated orbital notch, shallow and slender infraorbital series, broad opercle, and short and slender rib 4. It differs from the type species <i>Amyzon mentale</i> in having a shorter posteroventral process of the dentary and fewer dorsal fin rays. Given the differences from all known Eocene catostomid species, <i>Amyzon brevipinne</i> is herein assigned to a new genus as <i>Wilsonium brevipinne</i>. Phylogenetically, this species is resolved as the most basal taxon of Catostomidae. The small-sized fluvial specimens of <i>Wilsonium brevipinne</i> represent the first recognized dwarf catostomid species in the fossil record (maximum standard length ∼ 84 mm). It is also worth noting that <i>Wilsonium</i> gen. nov. differs from all known catostomids in the elongated orbital notch, shallow and slender infraorbital series and non-robust rib 4. These features are seen in some loaches and gyrinchelids. http://zoobank.org/urn:lsid:zoobank.org:pub:A185883A-68FC-4A7F-A103-889EE22ED134本研究基于新近采集的标本，对产自加拿大不列颠哥伦比亚省（British Columbia）艾伦比组（Allenby Formation）的始新世鲤形目（Cypriniformes）亚口鱼科（Catostomidae）化石鱼类开展了分类厘定与修订工作。该鱼类最初由科普（Cope）于1893年被认定为亚口鱼科成员，并被命名为短鳍似鳅鲤（*Amyzon brevipinne*）。威尔逊（Wilson）于1977年基于大量馆藏标本对该物种进行了全面的重新描述。新近采集的更多标本表明，该物种亟需开展系统性分类修订：其与所有已知似鳅鲤属（Amyzon）物种存在显著差异，具体特征包括狭长额骨搭配延长的眶切迹、浅而纤细的眶下骨列、宽大的鳃盖骨以及短而纤细的第4肋。该物种与模式种似鳅鲤（*Amyzon mentale*）的区别还包括：齿骨后腹突更短，背鳍鳍条数更少。鉴于该物种与所有已知始新世亚口鱼科物种均存在明显差异，本研究将短鳍似鳅鲤（*Amyzon brevipinne*）归入新属，命名为短鳍威尔逊鱼（*Wilsonium brevipinne*）。系统发育分析显示，该物种为亚口鱼科（Catostomidae）最基干的演化类群。此次发现的小型河流相标本（短鳍威尔逊鱼*Wilsonium brevipinne*）为化石记录中首个被确认的矮小型亚口鱼科物种，其最大标准体长约为84毫米。此外，威尔逊鱼属（*Wilsonium* gen. nov.）与所有已知亚口鱼科类群的区别还在于：具延长的眶切迹、浅而纤细的眶下骨列以及不粗壮的第4肋。相关分类注册号：http://zoobank.org/urn:lsid:zoobank.org:pub:A185883A-68FC-4A7F-A103-889EE22ED134